Department Of Chemical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

This work presents a critical analysis of 2D model of refueling a hydrogen storage tank containing MOF-5 adsorbent under cryogenic and room temperature conditions. Three isotherm models, viz. Unilan, modified Dubinin–Astakhov DA and Tóth, were fitted with experimental data of hydrogen adsorption from the literature, and their effect on refueling of adsorbent bed is analyzed. The choice of isotherm has the greatest impact on predicting refueling behavior, for both flow-through and end-flow (i.e., batch) systems. A comparison between the ideal gas assumption and virial equation of state indicates that the former reasonably captures the overall behavior at lower computational cost. Analysis of the role of momentum balance, solved as full Navier–Stokes model and with Darcy's approximation, indicates same hydrogen uptake in the adsorbent bed and only a minor difference in the predicted velocity profiles. Finally, effect of temperature-dependent physical properties of gas, adsorbent and walls is analyzed. © 2020 The Korean Society of Industrial and Engineering Chemistry

World University root node

Journal of Industrial and Engineering Chemistry

A critical analysis of transport models for refueling of MOF-5 based hydrogen adsorption system

Halide perovskites show incredible photovoltaic power conversion efficiency coupled with several hundreds of hours of device stability. However, their stability is poor in aqueous electrolyte media. Reported here is a vacancy ordered halide perovskite, Cs2PtI6, which shows extraordinary stability under ambient conditions (1 year), in aqueous media of extreme acidic (pH 1), basic (pH 13), and under electrochemical reduction conditions. It was employed as an electrocatalyst and photoanode for hydrogen production and water oxidation, respectively. The catalyst remains intact for at least 100 cycles of electrochemical cycling and six hours of hydrogen production at pH 1. Cs2PtI6 was employed as a photoanode for PEC water oxidation, and the material displayed a photocurrent of 0.8 mA cm−2 at 1.23 V (vs. RHE) under simulated AM1.5G sunlight. Using constant voltage measurement, Cs2PtI6 exhibited over 12 hours of PEC stability without loss of performance.

Cs
            2
            PtI
            6
            Halide Perovskite is Stable to Air, Moisture, and Extreme pH: Application to Photoelectrochemical Solar Water Oxidation

The patterns resulting from drying particle-laden sessile drops (for example, coffee rings, where the particles are concentrated more at the edge, and their complete suppression, where the particles are uniformly distributed throughout the pattern) have been well studied for more than two decades. For the ubiquitous instance of occurrence of drying of drops containing nonvolatile species (either dissolved or dispersed) on substrates oriented at different angles with respect to gravity, the investigation of resulting evaporative patterns has not received much attention. This mini-review addresses the need to investigate the drying of drops residing on inclined surfaces and highlights recent advances in this field. Copyright © 2020 American Chemical Society.

Fulltext

ACS Omega

Beyond Coffee Rings: Drying Drops of Colloidal Dispersions on Inclined Substrates

Dissolution rates of Ti, Zr, Nb and Ta in acidic fluoride media of different concentrations at various temperatures were measured by weight loss method, and were complemented by electrochemical measurements at room temperatures. A mathematical model to estimate the corrosion rate of these four valve metals based on the overall reaction mechanism for metal dissolution as well as H2 evolution is developed from the weight loss experiments. Valve metal dissolution process occurs through two independent pathways assisted by (HF2)− and equilibrium HF species. Except Ti, the dissolution of other valve metals studied are not significantly influenced by the H2 evolution reaction. Among the four metals evaluated, Nb offers the best corrosion resistance at high temperature and high HF concentration. The corrosion resistance of all four valve metals estimated from linear polarization, electrochemical spectroscopy and Tafel extrapolation in various concentrations of solutions match well. For Ti, dissolution rates calculated from Tafel extrapolation were lower than those based on weight loss experiments, while for Zr, Nb and Ta, they were mostly higher than those based on weight loss experiments.

Studies on Group IV and V Valve Metal Corrosion in Acidic Fluoride Media

Ultrathin polyethylenimine (PEI) interlayers are frequently used to reduce the work function of electrode materials; however, to exploit the full potential of this material for application in optoelectronic devices, further fundamental understanding is required. Here, it is demonstrated that intermixing of PEI deposited from water solution onto the conductive polymer poly(3,4-ethylene-dioxythiophene) (PEDOT):polystyrene sulfonate can be avoided by using anhydrous butanol as solvent. At the same time, this choice of solvent prevents de-doping of PEDOT and preserves the electrode's transparency. For inorganic electrode materials, i.e., ZnO and graphite, it is demonstrated that residual solvent in PEI films, present even after annealing in inert gas atmosphere, leads to significant surface dewetting, and thus inhomogeneity in terms of the morphology and work function. However, annealing in ultrahigh vacuum removes residual solvent, establishes homogenous surface coverage with PEI, and allows one to achieve the maximum work function reduction. For the transparent electron transport material ZnO, a record low work function value of 2.3 eV is achieved, which can enable the formation of ohmic contacts to most semiconductors.

Electrode Work Function Reduction by Polyethylenimine Interlayers: Choice of Solvent and Residual Solvent Removal for Superior Functionality

Proton exchange membrane (PEM) fuel cells are attractive because of advantages such as low-temperature operation, no emission of harmful gases and high efficiency. However, the bipolar plates used in the state-of-the-art planar architecture are costly and increase the dead weight of the cell. In addition, the flow channels in the planar fuel cell increase the difficulty in removing the water produced in the cathode during cell operation. Cylindrical PEM fuel cells, on the other hand, do not require bipolar plates and there is no need for precisely machined flow channels. Thus, cylindrical PEM fuel cells are cheap, efficient in water management, and possess higher volumetric and gravimetric power density compared to planar PEM fuel cells. The design of a cylindrical fuel cell is very simple, but the fabrication of the same is fairly complex. In this work, a novel cathode current collector design for cylindrical PEM fuel cell has been developed. The cell performance was limited by low open circuit voltage and high ohmic resistance. The open circuit voltage of the cell is increased from 0.85 V to 0.95 V using an acrylic based adhesive to seal the membrane edges. The contact resistance of the cell is reduced from 75 mOhm to 50 mOhm by increasing the contact pressure on the membrane electrode assembly and it is further reduced to 30 mOhm by gold coating the current collectors. Furthermore, a cumulative 40% increase in peak power has been achieved from the optimization of cathode rib width and hydrogen flow rate. The optimized cell delivered a current density of 400 mA/cm2 at 0.6 V and peak power of 2 W, which is appreciable considering the fact that the cell is air-breathing and operated with very minimal subsystems. © 2019 Hydrogen Energy Publications LLC

GENERAL

International Journal of Hydrogen Energy

Development of cylindrical PEM fuel cells with semi-cylindrical cathode current collectors

Drying of complex fluids is a fascinating subject of interest to several growing fields, for example, forensic science, lithography, printing and coating technologies. In this article, we report that the drying of charge stabilized colloidal dispersions between two parallel plates is a route to intriguing self-assembly patterns. We show that when the dispersions are dried in parallel plate confinement, particles deposit as spiral patterns after the complete evaporation of the solvent irrespective of the confinement spacing. The formation of such patterns is understood by analyzing the underlying three phase contact line dynamics during the drying process. Compared to the usual discrete stick-slip motion of the contact line, typically observed in several drying configurations, in the parallel plate drying configuration, the contact line is found to exhibit continuous stick-slip motion. The de-pinning of the contact line is found to occur only locally and is observed to propagate in both clockwise and anticlockwise directions, leading to the patterning of colloids as spirals. Furthermore, we show that while the number of turns in the spiral deposit is influenced by the dispersion volume and particle concentration, the spiral patterns form irrespective of the shape of the particles in the dispersion.&nbsp;

Soft Matter

Patterning of colloids into spirals via confined drying

The aim of this work is to develop insights into adsorption of hydrogen and carbon dioxide in a zeolitic imidazolate framework, ZIF-8, using high-pressure adsorption studies, adsorption isotherm model fitting, and DFT investigation of preferential adsorption sites and binding energies. The robustness of ZIF series metal–organic frameworks has drawn interest towards its utility in large scale applications in gas storage and separation. We use room temperature synthesis of ZIF-8 using DMF as a solvent, and benchmarked it against typical solvothermal synthesis. The resulting material is characterized using XRD, SEM, TG–DSC and N2 adsorption isotherm. High-pressure volumetric adsorption of the activated materials is conducted to analyze the hydrogen and carbon dioxide storage capacities up to 50 and 40&nbsp;bar, respectively. ZIF-8 shows maximum H2 storage capacity of 3.13 wt% at 50&nbsp;bar and 77&nbsp;K, and CO2 storage capacity of 46 wt% at 40&nbsp;bar and 300&nbsp;K. The parameters of Unilan adsorption isotherm are estimated from the equilibrium adsorption data and isosteric heats of adsorption for H2 and CO2 on ZIF-8 are computed. DFT calculations are used to obtain preferential adsorption sites of H2 and CO2. Adsorption enthalpy values were calculated from DFT as −&nbsp;7.08 and −&nbsp;25.98&nbsp;kJ/mol, respectively for H2 and CO2 at the most preferred sites. We found a close agreement between isosteric heat of adsorption of hydrogen (−&nbsp;4.68&nbsp;kJ/mol) and the enthalpy of hydrogen adsorption from DFT (−&nbsp;6.04&nbsp;kJ/mol) at 77&nbsp;K.

Department Of Chemistry

Adsorption of hydrogen and carbon dioxide in zeolitic imidazolate framework structure with SOD topology: experimental and modelling studies

Stability of oil-in-water emulsions under high pressure and high temperature (HPHT) conditions has a significant interest in upstream oil and gas industrial applications. Such emulsions are generally stabilized with surfactants, which are thermodynamically unstable under HPHT conditions. Alternate to surfactants, the addition of nanoparticles has emerged as a method for emulsion stabilization, known as Pickering emulsion. In this work, a comparative study of the stability of silica nanoparticle (Ludox CL) stabilized Pickering emulsion against surfactant SDS (sodium dodecyl sulfate) stabilized emulsion under HPHT conditions has been explored. The stability of the emulsions was measured in terms of change in emulsion droplet diameter. Subsequently, emulsion samples are aged under different pressure and temperature conditions in an aging cell for 24 hours. The emulsion mean droplet diameter increases with an increase in temperature. The magnitude of change in the mean droplet diameter of aged SDS stabilized emulsion is higher as compared to Ludox CL stabilized emulsion under varying pressure (0.1–10 MPa) and temperature (303–363 K). It can be concluded that Ludox CL stabilized emulsion shows better stability as compared to SDS stabilized emulsion under HPHT conditions. Hence, emulsion stabilized by Ludox CL nanoparticle may withstand harsh reservoir conditions and can be used for enhanced oil recovery applications.&nbsp;&nbsp;&nbsp;

Department of Ocean Engineering

Journal of Dispersion Science and Technology

Stability of nanoparticle stabilized oil-in-water Pickering emulsion under high pressure and high temperature conditions: comparison with surfactant stabilized oil-in-water emulsion

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil. © 2020 Institution of Engineering and Technology. All rights reserved.